1. Technical Field
The present invention relates to an electronic device which uses a secondary battery.
2. Related Art
For example, an electronic device which uses a secondary battery as a power source, such as an electronic timepiece including a solar cell (hereinafter, referred to as a “solar timepiece”), has been generally and widely used. If this type of electronic device is driven in a state where the electronic device is left in a dark place without charging the secondary battery, a power supply voltage is gradually reduced. If the power supply voltage in this type of electronic device falls below a lower limit value of a voltage which guarantees a normal operation (hereinafter, referred to as an operation-guaranteed voltage) for a controller such as a Central Processing Unit (CPU), a normal control cannot be performed, thereby bringing the electronic device into a runaway state in some cases. Even when charging for the power source and power consumption are performed in parallel, if a state continues where a charging current falls below a consumed current, there is also a possibility that the electronic device may be brought into the runaway state. In addition, when the charging for the power source and the power consumption are performed in parallel, the charging and the power consumption cause the power supply voltage to pulsate over the operation-guaranteed voltage, thereby causing a possibility that the occurrence of the runaway state and restoring from the runaway state may be repeated. Various techniques for preventing this repetition of the occurrence of the runaway state and the restoring from the runaway state (hereinafter, referred to as “continuation of the runaway state”) have been proposed in the related art. As an example, JP-A-2006-153669 discloses a technique. According to the technique disclosed in JP-A-2006-153669, when the power supply voltage falls below a voltage which is set to be higher than the operation-guaranteed voltage (hereinafter, referred to as a set voltage), a system is initialized by cyclically outputting an initializing signal for instructing the CPU to perform initializing, thereby preventing the continuation of the runaway state.
However, according to the technique disclosed in JP-A-2006-153669, when the power supply voltage falls below the set voltage due to a temporarily decreased voltage which is caused by a heavy load, the initializing signal is output, thereby causing a possibility that the system may be inadvertently initialized. For example, when the technique disclosed in JP-A-2006-153669 is applied to an alarm-installed solar timepiece, there is a disadvantage in that the system is initialized due to a temporarily decreased voltage which is caused by alarm sounding.